Assessment of in vitro effects of direct thrombin inhibitors and activated factor X inhibitors through clot waveform analysis.

AIMS: Clot waveform analysis (CWA) has been reported to extend the interpretation of clotting time measurement. The parameters obtained from successive derivatives of the clotting reaction curves reflect the rates of activation of individual coagulation factors, theoretically dissecting the cascade pathway. This study aims to assess the in vitro effects of direct thrombin inhibitors (DTIs) and activated factor X (FXa) inhibitors. METHODS: CWA was applied to the activated partial thromboplastin time (APTT) assay of plasma samples spiked with each drug. For CWA of APTT measurement curves (APTT-CWA), the positive mode of clotting reaction curves was defined as the direction towards fibrin generation. RESULTS: All the maximum positive values in the successive derivatives were decreased dependently on the concentrations of each drug. Moreover, the negative values in the second and third derivatives appeared putatively due to consumption of thrombin and factor FXa, respectively, to form complexes with plasma serine protease inhibitors. The decrease of the maximum negative values observed dependently on the concentrations of each drug appeared to be consistent with the decreased generation of thrombin and factor FXa. The analysis of Hill coefficients of each drug in the dose-response of changes in the APTT-CWA parameters revealed a difference in anticoagulant cooperativity between DTIs versus FXa inhibitors. CONCLUSIONS: The APTT-CWA demonstrated evidence for the blockade of thrombin-positive feedback by DTIs and FXa inhibitors and that for the differences in anticoagulant cooperativity between them. The results demonstrate the usability of CWA for assessment of anticoagulation and provide insights into direct anticoagulants.

[Use of a Delphi survey to assess the hospital economic impact of innovative products: The example of idarucizumab a dabigatran-specific reversal agent]. / Utilisation du questionnaire Delphi pour anticiper l'impact économique des innovations thérapeutiques à l'hôpital : application à l'idarucizumab, le nouvel agent de réversion spécifique au dabigatran.

OBJECTIVES: The economic impact of therapeutic innovations on the hospital patient management cannot be easily estimated. The objective of this study is to illustrate the use of a Delphi survey as a support tool to identify the changes following the use of idarucizumab in dabigatran-treated patients with uncontrolled/life-threatening bleeding or who required emergency surgery/urgent procedures. METHODS: The Delphi questionnaires have been administrated to 8 emergency physicians or anesthetists from 6 different hospital centers. Following the answers, an economic valorization has been carried out on every parameter on which a consensus was reached (at least 4 answers showing an identical trend). A mean management cost for each etiology with and without the use of idarucizumab has thus been identified. RESULTS: For gastro-intestinal and other life-threatening bleedings (excepted intracranial bleedings), the total management cost of the hospital stay was respectively 6058 € (-35%) and 6219 € (-34%) following the use of the reversal agent. The hospital management cost for intracranial bleeding is slightly increasing to 9790 € (+3%). The cost of a stay for emergency surgery decreases to 6962€ (-2%). CONCLUSIONS: This study shows a positive economic impact following the use of the dabigatran-specific reversal agent for patients with uncontrolled/life-threatening bleeding excepted in the case of intracranial bleeding. Moreover, it points out that a Delphi survey is an easy way to predict the hospital economic impact of a therapeutic innovation when no other evaluation is possible.

In-vitro assessment of the effect of dabigatran on thrombosis of adult and neonatal plasma: comparisons using thromboelastography and microscopic visualization of fibrin clot structure.

: Thromboelastography (TEG) is a global assay used for evaluating features of clot formation in vitro. Dabigatran is a reversible direct inhibitor of thrombin that has not been studied in neonates using a sophisticated global assay, such as TEG. Neonatal hemostasis differs from adult hemostasis in both quantitative and qualitative characteristics. Our aim was to compare the TEG clotting profile of neonatal and adult platelet-poor plasma when exposed to different concentrations of dabigatran. We used commercially collected adult pooled plasma and neonatal cord blood collected from placentas of healthy full term newborns. Platelet-poor plasma was isolated, pooled, and frozen. Prior to experiment, plasma was thawed and filtered. A reaction mixture of CaCl2, corn trypsin inhibitor, tissue factor, and dabigatran in imidazole buffer was mixed with plasma in a TEG cup. Time to clot initiation (R-time), speed of clot strengthening (α-angle), and maximum clot strength (maximal amplitude) were measured. Scanning electron microscopy was performed to evaluate fibrin clot structure. Without dabigatran, there was no significant difference in TEG measurements between neonatal and adult samples. However, neonatal plasma clotting with dabigatran had slower onset, slower speed, and weaker clots that were more porous with thicker fibers, compared with adult plasma clotting. Thus, neonatal plasma may be more sensitive to dabigatran as assessed by our in-vitro TEG study.

Laboratory Assessment of the Anticoagulant Activity of Direct Oral Anticoagulants: A Systematic Review.

BACKGROUND: Direct oral anticoagulants (DOACs) are the treatment of choice for most patients with atrial fibrillation and/or noncancer-associated venous thromboembolic disease. Although routine monitoring of these agents is not required, assessment of anticoagulant effect may be desirable in special situations. The objective of this review was to summarize systematically evidence regarding laboratory assessment of the anticoagulant effects of dabigatran, rivaroxaban, apixaban, and edoxaban. METHODS: PubMed, Embase, and Web of Science were searched for studies reporting relationships between drug levels and coagulation assay results. RESULTS: We identified 109 eligible studies: 35 for dabigatran, 50 for rivaroxaban, 11 for apixaban, and 13 for edoxaban. The performance of standard anticoagulation tests varied across DOACs and reagents; most assays, showed insufficient correlation to provide a reliable assessment of DOAC effects. Dilute thrombin time (TT) assays demonstrated linear correlation (r2 = 0.67-0.99) across a range of expected concentrations of dabigatran, as did ecarin-based assays. Calibrated anti-Xa assays demonstrated linear correlation (r2 = 0.78-1.00) across a wide range of concentrations for rivaroxaban, apixaban, and edoxaban. CONCLUSIONS: An ideal test, offering both accuracy and precision for measurement of any DOAC is not widely available. We recommend a dilute TT or ecarin-based assay for assessment of the anticoagulant effect of dabigatran and anti-Xa assays with drug-specific calibrators for direct Xa inhibitors. In the absence of these tests, TT or APTT is recommended over PT/INR for assessment of dabigatran, and PT/INR is recommended over APTT for detection of factor Xa inhibitors. Time since last dose, the presence or absence of drug interactions, and renal and hepatic function should impact clinical estimates of anticoagulant effect in a patient for whom laboratory test results are not available.

Analytical comparison of a US generic enoxaparin with the originator product: The focus on comparative assessment of antithrombin-binding components.

Enoxaparin sodium, a low-molecular-weight heparin (LMWH) prepared from porcine intestinal heparin, is widely used for the prevention and treatment of venous thromboembolism. The antithrombotic activity of heparin is mediated mainly through its activation of antithrombin (AT) and subsequent inhibition of coagulation factors. Heparin is a complex heteropolymer and the sulfation pattern of its alternating uronic acid and glucosamine sugar units is a major factor influencing its biological activity. The manufacturing process itself is associated with the introduction of exogenous microheterogeneities that may further affect its biological efficacy. This is important since enoxaparin is prepared by depolymerizing the heparin with the aim of optimizing its biological activity and safety. Changes during its manufacture could thus affect its biological activity and safety. The current study was performed to assess potential differences between the originator enoxaparin and a new generic enoxaparin commercialized by Teva. Heparinase digestion, AT affinity chromatography, gel permeation chromatography, anion exchange chromatography, and nuclear magnetic resonance methodologies were used. The results indicated differences in oligosaccharides related to the cleavage selectivity around the heparin AT-binding sequences of the Teva Enoxaparin Sodium Injection, USP and the originator Sanofi enoxaparin. These differences influence the strength of the AT-binding affinity of the individual oligosaccharides, their ability to activate AT and, therefore, the inhibitory potency on the proteases of the coagulation cascade. This study, together with other published analytical reports, describes specific compositional differences between generics and originator LWMHs. However, it is yet to be established whether such variations might have any clinical relevance.

Pharmacologic Therapies in Anticoagulation.

Anticoagulants are beneficial for prevention and treatment of venous thromboembolism and stroke prevention in atrial fibrillation. The development of target-specific oral anticoagulants is changing the landscape of anticoagulation therapy and created growing interest on this subject. Understanding the pharmacology of different anticoagulants is the first step to adequately treat patients with best available therapy while avoiding serious bleeding complications. This article reviews the pharmacology of the main anticoagulant classes (vitamin K antagonists, direct oral anticoagulants, and heparins) and their clinical indications based on evidence-based data currently available in the literature.

At-line nanofractionation with parallel mass spectrometry and bioactivity assessment for the rapid screening of thrombin and factor Xa inhibitors in snake venoms.

Snake venoms comprise complex mixtures of peptides and proteins causing modulation of diverse physiological functions upon envenomation of the prey organism. The components of snake venoms are studied as research tools and as potential drug candidates. However, the bioactivity determination with subsequent identification and purification of the bioactive compounds is a demanding and often laborious effort involving different analytical and pharmacological techniques. This study describes the development and optimization of an integrated analytical approach for activity profiling and identification of venom constituents targeting the cardiovascular system, thrombin and factor Xa enzymes in particular. The approach developed encompasses reversed-phase liquid chromatography (RPLC) analysis of a crude snake venom with parallel mass spectrometry (MS) and bioactivity analysis. The analytical and pharmacological part in this approach are linked using at-line nanofractionation. This implies that the bioactivity is assessed after high-resolution nanofractionation (6 s/well) onto high-density 384-well microtiter plates and subsequent freeze drying of the plates. The nanofractionation and bioassay conditions were optimized for maintaining LC resolution and achieving good bioassay sensitivity. The developed integrated analytical approach was successfully applied for the fast screening of snake venoms for compounds affecting thrombin and factor Xa activity. Parallel accurate MS measurements provided correlation of observed bioactivity to peptide/protein masses. This resulted in identification of a few interesting peptides with activity towards the drug target factor Xa from a screening campaign involving venoms of 39 snake species. Besides this, many positive protease activity peaks were observed in most venoms analysed. These protease fingerprint chromatograms were found to be similar for evolutionary closely related species and as such might serve as generic snake protease bioactivity fingerprints in biological studies on venoms.

Differential benefit risk assessment of DOACs in the treatment of venous thromboembolism: focus on dabigatran.

Venous thromboembolism includes deep vein thrombosis and pulmonary embolism and is a serious medical condition that requires anticoagulation as part of treatment. Currently, standard therapy consists of parenteral anticoagulation followed by a vitamin K antagonist (VKA). The pharmacokinetic and pharmacodynamic profiles of the direct oral anticoagulants (DOACs) differ from VKAs, which overcome some of the limitations of VKAs and have practical implications on their use in clinical situations. Dabigatran is a prodrug that undergoes primarily renal elimination and does not affect cytochrome P450 enzymes. Assays to quantify the degree of anticoagulation and the therapeutic level of DOAC are either unavailable for routine clinical use or require specific calibration. Routine monitoring of DOACs is not recommended at this time. Dabigatran, rivaroxaban, and apixaban are DOACs that have been studied for treatment of venous thromboembolism. Clinical trials comparing DOACs with standard therapy have shown them to be non-inferior for acute and extended therapy. Each DOAC has a unique benefit and harm profile that should be considered prior to use. The distinguishing characteristics of dabigatran include a requirement of parenteral anticoagulation prior to acute treatment, clinical trial results comparing it with a VKA for extended treatment, association with upper gastrointestinal adverse events, and increased risk of gastrointestinal bleed. Rivaroxaban is the only DOAC that has once-daily dosing while apixaban is the only DOAC that has lower risk of overall, major, and gastrointestinal bleeding compared with VKA. A common drawback of DOACs is the lack of an available reversal agent. Clinical trials of reversal agents are ongoing and one application for approval has been submitted to the US Food and Drug Administration. Selection of a DOAC for acute and extended therapy requires a shared decision-making approach that includes a comprehensive assessment of the benefits and harms of each individual DOAC.

Current and emerging strategies in the management of venous thromboembolism: benefit-risk assessment of dabigatran.

Venous thromboembolism (VTE) is a disease state that carries significant morbidity and mortality, and is a known cause of preventable death in hospitalized and orthopedic surgical patients. There are many identifiable risk factors for VTE, yet up to half of VTE incident cases have no identifiable risk factor and carry a high likelihood of recurrence, which may warrant extended therapy. For many years, parenteral unfractionated heparin, low-molecular weight heparin, fondaparinux, and oral vitamin K antagonists (VKAs) have been the standard of care in VTE management. However, limitations in current drug therapy options have led to suboptimal treatment, so there has been a need for rapid-onset, fixed-dosing novel oral anticoagulants in both VTE treatment and prophylaxis. Oral VKAs have historically been challenging to use in clinical practice, with their narrow therapeutic range, unpredictable dose responsiveness, and many drug-drug and drug-food interactions. As such, there has also been a need for novel anticoagulant therapies with fewer limitations, which has recently been met. Dabigatran etexilate is a fixed-dose oral direct thrombin inhibitor available for use in acute and extended treatment of VTE, as well as prophylaxis in high-risk orthopedic surgical patients. In this review, the risks and overall benefits of dabigatran in VTE management are addressed, with special emphasis on clinical trial data and their application to general clinical practice and special patient populations. Current and emerging therapies in the management of VTE and monitoring of dabigatran anticoagulant-effect reversal are also discussed.

Tolerability and Acceptability of Non-Vitamin K Antagonist Oral Anticoagulants in Atrial Fibrillation: Systematic Review and Meta-Analysis.

BACKGROUND: The non-vitamin K antagonist oral anticoagulants (NOACs) overcame some limitations of vitamin K antagonists (VKAs), and are at least as effective in stroke prevention, with an additional decrease of intracranial bleeding risk. The transferability of these benefits to the real world requires tolerability (related to adverse events) and acceptability (drug discontinuation) profiles at least similar to VKAs. METHODS: We performed a systematic review with meta-analysis of randomized controlled trials (RCTs) evaluating NOACs versus VKAs in patients with non-valvular atrial fibrillation (AF). Studies were searched in April 2015 through MEDLINE, the Cochrane Collaboration's Database, Health Technology Assessment (HTA), Web of Science, and regulatory agencies' documents. Serious adverse events (SAEs) as well as drug-related and patient-related discontinuation rates were the outcomes of interest. Random-effects meta-analysis was performed, and the results expressed as risk ratios (RRs) and 95 % confidence intervals (CIs). Heterogeneity was evaluated with I (2) test. RESULTS: Five RCTs evaluating four NOACs (apixaban, dabigatran, edoxaban, and rivaroxaban) and 72,720 patients were included. Overall, NOACs were associated with a 4 % risk reduction of SAEs (95 % CI 2-6; I (2) = 0 %). Drug-related and patient-related discontinuation rates were similar between NOACs and VKAs (RR 1.03 [0.88-1.21] and RR 0.99 [0.89-1.10], respectively). Significant heterogeneity (I (2) ≥ 75 %) was found among studies results, which could be, at least partially, explained by the findings of the open-label dabigatran trial. CONCLUSIONS: NOACs were associated with a small, yet significant, risk reduction of SAEs in patients with AF. NOACs' drug-related and patient-related acceptability profiles were similar to those for VKAs. The results were heterogeneous mainly because of the increased rate of discontinuation associated with dabigatran. Pragmatic trials and cohort studies should be conducted to further address these important clinical questions.

Dabigatran for the prevention of stroke and systemic embolism in atrial fibrillation: A NICE single technology appraisal.

The National Institute for Health and Clinical Excellence (NICE) invited the manufacturer of dabigatran etexilate (Boehringer Ingelheim Ltd, UK) to submit evidence for the clinical and cost-effectiveness of this drug for the prevention of stroke and systemic embolism in patients with non-valvular atrial fibrillation (AF) as part of the NICE single technology appraisal process. The Centre for Reviews and Dissemination and the Centre for Health Economics at the University of York were commissioned to act as the evidence review group (ERG). This article presents a summary of the manufacturer's submission, the ERG report and the subsequent development of NICE guidance for the use of dabigatran within the UK National Health Service. Dabigatran was granted marketing authorisation by the European Medicines Agency for a sequential dosing regimen (DBG sequential), in which patients under 80 years are treated with dabigatran 150 mg twice daily (DBG150) and patients 80 years and over are given dabigatran 110 mg twice daily (DBG110). NICE decisions are bound by the marketing authorisation; therefore, the decision problem faced by the committee was whether the DBG sequential regimen was effective and cost-effective compared with warfarin or aspirin for patients with non-valvular AF and one or more risk factors. The RE-LY trial, a large multi-centre non-inferiority randomised clinical trial, was the primary source of clinical evidence. DBG150 was shown to be non-inferior, and subsequently superior to warfarin, for the primary outcome of all stroke/systemic embolism. DBG110 was found to be non-inferior to warfarin. Results were presented for a post hoc subgroup analysis for patients under and over 80 years of age, where DBG110 showed a statistically significant reduction of haemorrhagic stroke and intracranial haemorrhage in comparison to warfarin in patients over 80 years of age. This post hoc subgroup analysis by age was the basis for the licensed DBG sequential regimen. The economic evaluation compared the costs and outcomes of DBG110, DBG150 and DBG sequential against warfarin, aspirin, and aspirin plus clopidogrel. Across the three dosing regimens, dabigatran was associated with greater costs and better health outcomes than warfarin; however, DBG150 offered the most benefits and dominated DBG110 and DBG sequential (i.e. less costly and more effective). The cost-effectiveness of DBG150 was less favourable for patients well controlled on warfarin. In the first appraisal meeting, the committee issued a 'minded no' decision until additional analyses on the licensed DBG sequential regimen were presented by the manufacturer. These additional analyses indicated that the incremental cost-effectiveness ratio (ICER) of the DBG sequential regimen compared with warfarin ranged from £8,388 to £18,987 per quality-adjusted life year (QALY) gained depending on the level of monitoring costs assumed for warfarin. Patients on warfarin would need to be within therapeutic range 83-85 % of the time for the ICER to exceed £30,000 per additional QALY. Following consideration of the additional evidence and the responses from a large number of consultees and commentators, the committee recommended dabigatran as DBG sequential as an option for the prevention of stroke and systemic embolism in people with non-valvular AF with one or more risk factors for ischaemic stroke.

Advantages of direct thrombin inhibition in high- and low-risk patients.

For an anticoagulant to replace heparin (and possibly glycoprotein IIb/IIIa inhibitors) for the interventional cardiologist, it must be proven to be useful in preventing ischemic complications and minimize bleeding risk in low- and high-risk patients in the settings of percutaneous coronary interventions (PCI), acute coronary syndromes (ACS) and acute myocardial infarction (AMI). The optimal agent will also streamline care and be cost effective. Bivalirudin has desirable pharmacokinetic properties and has been shown to improve outcomes as an alternative to heparin and glycoprotein IIb/IIIa inhibitors in both high- and low-risk patients undergoing urgent and elective PCI. Ongoing studies are investigating the utility of this agent in patients with ACS and AMI.

Direct thrombin inhibitors.

Bivalent direct thrombin inhibitors reduce ischemic risk compared to heparin. Results from randomized, double-blind clinical trials have demonstrated that bivalirudin is superior to heparin alone and as effective as heparin plus routine glycoprotein (GP) IIb/IIIa therapy for the prevention of ischemic events with a statistically significant reduction in the rate of in-hospital major bleeding.

Bivalirudin: a direct thrombin inhibitor.

BACKGROUND: Studies of the anticoagulant effects of hirudin, which is derived from the saliva of the leech Hirudo medicinalis, led to the development of compounds that can directly inhibit thrombin activity without the need for additional cofactors. One of these is the direct thrombin inhibitor bivalirudin, which has recently been approved by the US Food and Drug Administration for use as an anticoagulant in patients with unstable angina undergoing percutaneous transluminal coronary angioplasty. OBJECTIVE: This is a review of the pharmacologic properties, efficacy, tolerability, and potential cost-effectiveness of bivalirudin in the treatment of ischemic coronary syndromes. METHODS: Articles were identified by searches of MEDLINE (1966-September 2001), International Pharmaceutical Abstracts (1970-September 2001), and the Iowa Drug Information Service (1966-September 2001) using the terms bivalirudin and Hirulog. The reference lists of retrieved articles were also reviewed for relevant articles. RESULTS: Bivalirudin is a synthetic polypeptide that directly inhibits thrombin by binding simultaneously to its active catalytic site and its substrate recognition site. After intravenous administration, peak plasma concentrations occur in 2 minutes. In patients given a 1.0-mg/kg bolus followed by a 2.5-mg/kg per hour infusion, a median activated clotting time of 346 seconds is achieved with little interpatient or intrapatient variability. Clearance of bivalirudin occurs through a combination of renal elimination and proteolytic cleavage, and doses may need to be decreased in the presence of renal dysfunction. In patients undergoing percutaneous coronary interventions, bivalirudin has been associated with equivalent efficacy but lower bleeding rates (P < 0.001) than unfractionated heparin (UFH). Data from the Hirulog Early Reperfusion/Occlusion-2 study suggest no reduction in mortality with bivalirudin compared with heparin when either is added to aspirin and streptokinase in patients with acute myocardial infarction, despite a lower reinfarction rate (P < 0.001). Experience with bivalirudin in patients with unstable angina and heparin-induced thrombocytopenia (HIT), as well as in patients receiving glycoprotein IIb/IIIla inhibitors, is limited. The differences in bleeding rates between bivalirudin and heparin in published clinical trials probably reflect differences in levels of anticoagulation achieved in comparator groups. CONCLUSIONS: Given its high cost, bivalirudin should be reserved for use as an alternative to UFH, primarily in patients with HIT, until clinical trials have more clearly demonstrated its benefits in terms of efficacy or safety.

Argatroban: a direct thrombin inhibitor for heparin-induced thrombocytopenia and other clinical applications.

Argatroban, a direct thrombin inhibitor derived from arginine, is an effective anticoagulant indicated for prophylaxis or treatment of thrombosis in patients with heparin-induced thrombocytopenia (HIT). Argatroban has been used as an alternative anticoagulant in patients with HIT in various clinical conditions including interventional cardiovascular procedures that require anticoagulation. Satisfactory clinical outcomes with acceptable complications have been reported in these patients. Whether argatroban offers additional clinical advantage over conventional heparin therapy in patients without HIT remains unclear. Argatroban has been evaluated as an alternative anticoagulant to replace heparin in various clinical studies, especially in patients with coronary artery disease or cerebral vascular disease. To date, it remains unclear if argatroban is more effective than heparin, although the agent seems to cause less bleeding complications. This article reviews the pharmacology of argatroban and its clinical application beyond the management of HIT, with particular emphasis on interventional cardiology procedure, acute myocardial infarction, unstable angina pectoris, cerebral thrombosis or ischemic stroke, peripheral obstructive arterial disease, and extracorporeal circulation.

Role of extracellular ionized calcium in the in vitro assessment of GPIIb/IIIa receptor antagonists.

Several preclinical studies have found a poor correlation between the ex vivo platelet inhibitory potency and the in vivo antithrombotic efficacy of GPIIb/IIIa receptor antagonists. The present study was designed to examine the differential in vitro potencies of c7E3, MK-383, DMP-728, and SM-20302 in inhibiting ex vivo platelet aggregation under normocalcemic and hypocalcemic conditions. Human blood was collected in either trisodium citrate (0. 37%) or PPACK (20 microg/mL). Platelet aggregation assays were performed in platelet-rich plasma from citrate-anticoagulated blood (cPRP) and PPACK-anticoagulated blood (pPRP) using ADP (20 microM) and TRAP (10 microM) as agonists in the presence of c7E3, MK-383, DMP-728, or SM-20302. The concentration of ionized calcium in cPRP was 16-19 times lower than that in pPRP. The IC(50) of c7E3 for inhibiting ADP-induced platelet aggregation in cPRP (2.76 +/- 0.11 microg/mL) was 1.6 times lower than that in pPRP (4.46 +/- 0.48 microg/mL; P < 0.05). Similarly, the IC(50) for c7E3 for inhibiting TRAP-induced platelet aggregation in cPRP (4.52 +/- 0.34 microg/mL) was 1.7 times lower than that in pPRP (7.69 +/- 0.43 microg/mL; P < 0.05). MK-383, DMP-728, and SM-20302 also demonstrated 1.96-, 1.15-, and 1.43-fold lower IC(50) values, respectively, in cPRP as compared with pPRP. Chelation of ionized calcium in pPRP led to a progressive increase in platelet inhibition by all the antagonists. These results suggest that the observed in vitro inhibitory potency of a GPIIb/IIIa receptor antagonist is markedly enhanced when trisodium citrate is used as an anticoagulant to collect blood for ex vivo assay. These findings indicate that dosing regimens for GPIIb/IIIa receptor antagonists based on the platelet inhibition profile in citrate may provide misleading information with respect to their true in vivo antithrombotic efficacy.

Assessment of the potential pharmacokinetic and pharmacodynamic interactions between erythromycin and argatroban.

Argatroban, a direct thrombin inhibitor, is metabolized in vitro by CYP3A4/5 and therefore may be susceptible to clinically relevant CYP3A drug interactions. The effect of erythromycin, a potent CYP3A4/5 inhibitor, on the pharmacokinetics and pharmacodynamics of argatroban was evaluated in 14 healthy male volunteers in an open-label, crossover study with a 5-day washout between regimens. Argatroban 1 microgram/kg/min was infused alone for 5 hours (regimen A) and again on day 6 of a 7-day oral regimen of 500 mg erythromycin four times daily (regimen B). Serial blood samples for the determination of activated partial thromboplastin time (aPTT) and argatroban concentrations were collected for up to 48 hours following infusion. Mean values for argatroban area under the concentration-time curves (AUC0-inf), maximum concentration (Cmax), and half-life (t1/2) were similar between regimens. Mean aPTT values were not affected significantly by the concomitant administration of argatroban and erythromycin compared to argatroban alone. No serious adverse events or bleeding episodes occurred during the study. These results suggest that oxidative metabolism by CYP3A4/5 is unlikely to be an important in vivo elimination pathway for argatroban. Therefore, coadministration of CYP3A4/5 inhibitors should not require a modification in the dosage of argatroban.

Antithrombin agents as anticoagulants and antithrombotics. Implications in drug development.

Synthetic and recombinant thrombin inhibitors have undergone several clinical evaluations for thrombotic and cardiovascular indications. While the initial trials were focused in coronary indications, more recently, these agents are also developed for the prophylaxis and therapeutic management of thromboembolic disorders. Hirudin, PEG-hirudin and argatroban are in advanced clinical development. Recombinant hirudin has been approved in Europe as a substitute anticoagulant for the management of HIT patients. Several additional clinical trials are currently carried out to demonstrate the usefulness of these agents in thrombotic and cardiovascular indications. Despite these developments such issues as dosage optimization, laboratory monitoring, neutralization and drug interactions require additional studies for the optimal development of these drugs.